I was playing on a server the other day on ATCS, and found myself continually getting trapped in my own base (human) by line of turrets and teslas. Since aliens can place their defenses on walls and ceilings, wouldn't it be an idea to have some sort of overhead defence for humans? My idea is to have a "UAV" which hovers around the base and is able to shoot at aliens without blocking base access.
Pros
Doesn't block access to and from the base like teslas and turrets often do.
Can cover a larger area than a turret since it can move around slightly.
Has the same firepower as a turret.
Not so easily destroyed by a Tyrant on a mad rampage (If placed well).
Cons
Has a relatively easy to attack control station which must be placed on the ground.
Requires a Defence Computer to function (Otherwise it will return to it's control station).
More costly than other defenses.
Since the guns are on the underside, it must be above or level with it's target (could be easily evaded by Marauders and Dragoons)
Essentially it's like an airborne turret, which can move around within a certain distance of its control station (a pad on the floor) It wouldn't be able to defend a base by itself, since it makes a fairly easy target for sniping and can be evaded by getting above it, so it would need to be backed up by other defenses. It could cost about 12 - 14 BP, and be unlocked at Stage 3.
I recently downloaded Blender, and with a little more practice I'll hopefully be able to model this. Until then, here are some hastily (and therefore poorly) drawn sketches:
... Stupid imageshack...
I'll post them later.